1. Field of the Invention
The present invention relates to transformers and more particularly, to an improved transformer structure, which provides an extended creepage distance at the secondary side to prevent formation of a potential difference and to enhance the voltage resistance strength.
2. Description of the Related Art
FIG. 7 illustrates a conventional high frequency transformer, which comprises an electrically insulative bobbin A, and two ferrite cores B. The bobbin A has wound thereon a primary winding A1 and a secondary winding A2. The bobbin A further has a plurality of partition flanges A21 that divide the secondary winding A2 into multiple secondary winding portions A24. The partition flanges A21 have a respective notch A22 at the same side for the passing of the wire of the secondary winding A2. Further, one vacant space A23 is defined between two partition flanges A21 around the periphery of the bobbin A corresponding to the connection area between the two ferrite cores B to reduce influence of magnetic field and to lower transformer loss.
FIG. 8 shows a double bobbin type high frequency transformer according to the prior art. According to this design, the transformer comprises two bobbins A, each bobbin A having wound thereon a primary winding A1 and a secondary winding A2, two first ferrite cores C1 respectively and axially inserted through the bobbins A, and an I-shaped second ferrite core C set between the two bobbins A with its two distal ends stopped between the first ferrite cores C1. The two first ferrite cores C1 form with the second ferrite core C two magnetic loops Ca and Cb. Because these two magnetic loops Ca and Cb commonly go through the second ferrite core C, they interfere with each other, resulting in unequal amount of electric current at the two lamp tubes that are respectively coupled to the output ends of the secondary windings A2 at the bobbins A, and therefore the two lamp tubes will have different brightness and the working life of the lamp tubes will be shortened.
The aforesaid prior art designs have the common drawbacks as follows:    1. When winding an wire on the bobbin A for the secondary winding A2, the wire must bridge each partition flange A21. When the shared voltage is excessively high, a potential different will occur at the bridging area to cause charging and discharging actions and to further produce an electric arc effect. In this case, the transformer may be burned out.    2. Bridging of the wire over the partition flanges A21 of the bobbin A may cause the secondary winding A2 to produce a potential difference that affects the voltage resistance of the transformer, thereby shortening the working life of the transformer.
Therefore, it is desirable to provide a transformer that eliminates the aforesaid drawbacks.